function c = uhel(e1, n1, n2)
%c = uhel(e1, n1, n2)
%vrati uhel sevreny prusecnicemi rovin urcenych normalami n1 a n2 s rovinou
%urcenou normalou e1
 c=acos(abs( normc(cross(n1, e1))'*normc(cross(n2, e1)) ) )*180/pi;
end